This proposed research is directed toward the extraction, purification and identification of the type-specific antigens of Chlamydia trachomatis. Previous experiments have indicated that a more thorough knowledge of these antigens may be important in the development of a vaccine for the prevention of trachoma. Isolation of these antigens would also simplify and clarify the serotyping of chlamydial isolates from trachoma endemic areas. A type-specific neutralization test, currently in use in this laboratory, will be further refined and along with the complement-fixation and fluorescent antibody tests will be used in studying the antigens of C. trachomatis types A, B, and C. An assay based on the solubilization of a radioactive label from neutralized chlamydia will be developed, and proposed experiments will demonstrate a correlation between loss of viability and solubilization of label. Antigens will be isolated from chlamydia at various stages of the life cycle and from purified envelopes. Isolated antigens will be tested for inhibition in the neutralization, complement-fixation and fluorescent antibody tests and active fractions will be tested as immunogens in mice and rabbits. Type-specific antibody, which will be purified by immunoabsorption and obtained by immunization of laboratory animals with purified antigens, will be tested for reactivity against homologous and heterologous trachoma types. Cells infected with trachoma strains will be examined for chlamydial antigens on host cell surfaces.